July 26 (Reuters) - More cracks have emerged among Iran's conservatives, after renewed opposition clamour over a disputed June 12 election. Both sides are targeting hardline President Mahmoud Ahmadinejad on the eve of his second term.

The death in prison of the son of an aide to Mohsen Rezaie, a defeated conservative candidate, reported by a reformist website on Saturday, could stoke what is already Iran's worst internal conflict for 30 years.

Here are some questions and answers on what direction the political storm might take and the challenges it poses to Ahmadinejad and Iran's Supreme Leader Ayatollah Ali Khamenei.

WHAT ARE THE OPPOSITION'S LATEST MOVES?

Defeated presidential candidates Mirhossein Mousavi and Mehdi Karoubi, backed by reformist former President Mohammad Khatami, still say the vote was rigged, defying Khamenei who has endorsed the result and demanded an end to protests.

On Saturday, the three men urged senior clerics to help secure the release of people detained after the election. Rights groups say hundreds have been jailed, including prominent reformists, journalists, academics and lawyers.

Karoubi, an ex-parliament speaker, wrote to the intelligence minister and accused the secret police of subjecting detainees in illegal centres to mental torture and physical threat.

Mousavi and Karoubi released a letter on Sunday asking the Interior Ministry to authorise a silent ceremony in Tehran to commemorate those killed in the unrest, without setting a date.

Mousavi, a moderate who was prime minister in the 1980s and who emerged as Ahmadinejad's main election challenger, has vowed to set up a new political front to "preserve people's votes".

HOW HAS THE GOVERNMENT RESPONDED?

The government has accused its critics of inciting "riots" on behalf of Iran's Western enemies and blamed them for post-election bloodshed in which it says 20 people were killed. Reformists and rights groups put the death toll much higher.

Some hardline clerics have demanded that Mousavi and Karoubi be tried on charges that could carry the death penalty.

Khamenei, having rejected calls for the election result to be annulled or re-examined, is expected to confirm Ahmadinejad as president soon. Parliament will then swear him in.

WHAT CHALLENGES FACE KHAMENEI?

The supreme leader has the last word on affairs of state in Iran's blend of clerical rule and republican institutions.

But Khamenei's Friday prayer sermon on June 19 failed to silence Mousavi and others who said the election was a fraud and that Ahmadinejad's next government would be illegitimate.

The religious establishment itself is divided. Many senior Shi'ite clerics have refrained from congratulating Ahmadinejad.

Akbar Hashemi Rafsanjani, an influential former president and heavyweight of the 1979 Islamic Revolution, helped embolden the opposition in a July 17 sermon in which he said Iran was in crisis, and demanded an end to detentions and press curbs.

Khamenei thus faces an unprecedented challenge to his authority from senior politicians and clerical figures. So far, he has made no concessions to the opposition, nor has he ordered even harsher repression, such as the arrest of its leaders.

WHAT CHALLENGES FACE AHMADINEJAD?

The fiery president is backed by hardline authorities and the elite Revolutionary Guard, with its Basij religious militia, but his support base elsewhere appears to have narrowed.

If confirmed, he will enter his second term on the back of a bitterly contested election whose outcome prompted hundreds of thousands of Iranians to take to the streets in protest.

The dissent may have tarnished Ahmadinejad's appeal even to his admirers abroad who share his hostility to the West. It has also dampened any prospect of dialogue with the United States to calm tensions over Iran's disputed nuclear programme.

Surprisingly, Ahmadinejad has also incurred the wrath of hardline conservatives enraged by his choice of his son-in-law, Esfandiar Rahim Mashaie, as his first vice president.

In a humiliating setback, Khamenei publicly forced Ahmadinejad to cancel the appointment of Mashaie, who was once quoted as saying Iran was friendly with everyone, even Israeli. (Writing by Alistair Lyon; editing by Robert Woodward)

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